The new FindPython-based variant of the CMake scripts caches information
about the chosen Python version that can become stale. For example,
suppose I configure a simple pybind11-based project as follows

```
cmake -S . -B build -GNinja -DPython_ROOT=<path to python 3.8>
```

which will generate `my_extension.cpython-38-x86_64-linux-gnu.so`.
A subsequent change to the python version like

```
cmake -S . -B build -GNinja -DPython_ROOT=<path to python 3.9>
```

does not update all necessary build system information. In particular,
the compiled file is still called
`my_extension.cpython-38-x86_64-linux-gnu.so`.

This commit fixes the problem by detecting changes in
`Python_EXECUTABLE` and re-running Python as needed.

Note that the previous way of detecting Python does not seem to be
affected, it always specifies the right suffix.

* Add make_value_iterator (#3271)

* Add make_value_iterator

This is the counterpart to make_key_iterator, and will allow
implementing a `value` method in `bind_map` (although doing so is left
for a subsequent PR).

I made a few design changes to reduce copy-and-paste boilerplate.
Previously detail::iterator_state had a boolean template parameter to
indicate whether it was being used for make_iterator or
make_key_iterator. I replaced the boolean with a class that determines
how to dereference the iterator. This allows for a generic
implementation of `__next__`.

I also added the ValueType and Extra... parameters to the iterator_state
template args, because I think it was a bug that they were missing: if
make_iterator is called twice with different values of these, only the
first set has effect (because the state class is only registered once).
There is still a potential issue in that the *values* of the extra
arguments are latched on the first call, but since most policies are
empty classes this should be even less common.

* Add some remove_cv_t to appease clang-tidy

* Make iterator_access and friends take reference

For some reason I'd accidentally made it take a const value, which
caused some issues with third-party packages.

* Another attempt to remove remove_cv_t from iterators

Some of the return types were const (non-reference) types because of the
pecularities of decltype: `decltype((*it).first)` is the *declared* type
of the member of the pair, rather than the type of the expression. So if
the reference type of the iterator is `pair<const int, int> &`, then the
decltype is `const int`. Wrapping an extra set of parentheses to form
`decltype(((*it).first))` would instead give `const int &`.

This means that the existing make_key_iterator actually returns by value
from `__next__`, rather than by reference. Since for mapping types, keys
are always const, this probably hasn't been noticed, but it will affect
make_value_iterator if the Python code tries to mutate the returned
objects. I've changed things to use double parentheses so that
make_iterator, make_key_iterator and make_value_iterator should now all
return the reference type of the iterator. I'll still need to add a test
for that; for now I'm just checking whether I can keep Clang-Tidy happy.

* Add back some NOLINTNEXTLINE to appease Clang-Tidy

This is favoured over using remove_cv_t because in some cases a const
value return type is deliberate (particularly for Eigen).

* Add a unit test for iterator referencing

Ensure that make_iterator, make_key_iterator and make_value_iterator
return references to the container elements, rather than copies. The
test for make_key_iterator fails to compile on master, which gives me
confidence that this branch has fixed it.

* Make the iterator_access etc operator() const

I'm actually a little surprised it compiled at all given that the
operator() is called on a temporary, but I don't claim to fully
understand all the different value types in C++11.

* Attempt to work around compiler bugs

https://godbolt.org/ shows an example where ICC gets the wrong result
for a decltype used as the default for a template argument, and CI also
showed problems with PGI. This is a shot in the dark to see if it fixes
things.

* Make a test constructor explicit (Clang-Tidy)

* Fix unit test on GCC 4.8.5

It seems to require the arguments to the std::pair constructor to be
implicitly convertible to the types in the pair, rather than just
requiring is_constructible.

* Remove DOXYGEN_SHOULD_SKIP_THIS guards

Now that a complex decltype expression has been replaced by a simpler
nested type, I'm hoping Doxygen will be able to build it without issues.

* Add comment to explain iterator_state template params

* fix: regression in #3271

Co-authored-by: Bruce Merry <1963944+bmerry@users.noreply.github.com>

This reverts commit ee0c5ee4.

Bumps [jwlawson/actions-setup-cmake](https://github.com/jwlawson/actions-setup-cmake) from 1.10 to 1.11.
- [Release notes](https://github.com/jwlawson/actions-setup-cmake/releases)
- [Commits](https://github.com/jwlawson/actions-setup-cmake/compare/v1.10...v1.11)

---
updated-dependencies:
- dependency-name: jwlawson/actions-setup-cmake
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <support@github.com>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

* Adding nullptr slices

Using example from #1095

Some fixes from @wjakob's review

Stop clang-tidy from complaining

New proposal for py::slice constructor

Eric's suggested changes: simplify testing; shift def's

* chore: drop MSVC pragma (hopefully unneeded)

* Apply suggestions from code review

* Apply blacken-docs and fix language-hints

* Add blacken-docs pre-commit hook

* Add pycln pre-commit hook

* Enable a few builtin hooks

* Black no longer ignores pyi files

* Add make_value_iterator

This is the counterpart to make_key_iterator, and will allow
implementing a `value` method in `bind_map` (although doing so is left
for a subsequent PR).

I made a few design changes to reduce copy-and-paste boilerplate.
Previously detail::iterator_state had a boolean template parameter to
indicate whether it was being used for make_iterator or
make_key_iterator. I replaced the boolean with a class that determines
how to dereference the iterator. This allows for a generic
implementation of `__next__`.

I also added the ValueType and Extra... parameters to the iterator_state
template args, because I think it was a bug that they were missing: if
make_iterator is called twice with different values of these, only the
first set has effect (because the state class is only registered once).
There is still a potential issue in that the *values* of the extra
arguments are latched on the first call, but since most policies are
empty classes this should be even less common.

* Add some remove_cv_t to appease clang-tidy

* Make iterator_access and friends take reference

For some reason I'd accidentally made it take a const value, which
caused some issues with third-party packages.

* Another attempt to remove remove_cv_t from iterators

Some of the return types were const (non-reference) types because of the
pecularities of decltype: `decltype((*it).first)` is the *declared* type
of the member of the pair, rather than the type of the expression. So if
the reference type of the iterator is `pair<const int, int> &`, then the
decltype is `const int`. Wrapping an extra set of parentheses to form
`decltype(((*it).first))` would instead give `const int &`.

This means that the existing make_key_iterator actually returns by value
from `__next__`, rather than by reference. Since for mapping types, keys
are always const, this probably hasn't been noticed, but it will affect
make_value_iterator if the Python code tries to mutate the returned
objects. I've changed things to use double parentheses so that
make_iterator, make_key_iterator and make_value_iterator should now all
return the reference type of the iterator. I'll still need to add a test
for that; for now I'm just checking whether I can keep Clang-Tidy happy.

* Add back some NOLINTNEXTLINE to appease Clang-Tidy

This is favoured over using remove_cv_t because in some cases a const
value return type is deliberate (particularly for Eigen).

* Add a unit test for iterator referencing

Ensure that make_iterator, make_key_iterator and make_value_iterator
return references to the container elements, rather than copies. The
test for make_key_iterator fails to compile on master, which gives me
confidence that this branch has fixed it.

* Make the iterator_access etc operator() const

I'm actually a little surprised it compiled at all given that the
operator() is called on a temporary, but I don't claim to fully
understand all the different value types in C++11.

* Attempt to work around compiler bugs

https://godbolt.org/ shows an example where ICC gets the wrong result
for a decltype used as the default for a template argument, and CI also
showed problems with PGI. This is a shot in the dark to see if it fixes
things.

* Make a test constructor explicit (Clang-Tidy)

* Fix unit test on GCC 4.8.5

It seems to require the arguments to the std::pair constructor to be
implicitly convertible to the types in the pair, rather than just
requiring is_constructible.

* Remove DOXYGEN_SHOULD_SKIP_THIS guards

Now that a complex decltype expression has been replaced by a simpler
nested type, I'm hoping Doxygen will be able to build it without issues.

* Add comment to explain iterator_state template params

updates:
- [github.com/psf/black: 21.8b0 → 21.9b0](https://github.com/psf/black/compare/21.8b0...21.9b0)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* Enable defining custom __new__

* See if xfail needed

* Qualify auto self

* Unconditionally defining PYBIND11_DISABLE_NEW_STYLE_INIT_WARNING. Returning pointer from "__init__" instead of reference.

* Use new style __init__

* Simplify __new__ creation

* Reviewer suggestions

* Match indentation

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

* Eliminate duplicate TLS keys for loader_life_support stack

This revises the existing fix for
https://github.com/pybind/pybind11/issues/2765 in
https://github.com/pybind/pybind11/pull/3237 to reduce the amount of
TLS storage used.

The shared TLS key is stored in two different ways, depending on
`PYBIND11_INTERNALS_VERSION`.  If `PYBIND11_INTERNALS_VERSION ==
4` (as is currently set), the TLS key is stored in the
`internal::shared_data` map to avoid breaking ABI compatibility.  If
`PYBIND11_INTERNALS_VERSION > 4`, the TLS key is stored directly in
the `internals` struct.

* Fix test_pytypes.py::test_issue2361 failure on PyPy3.7

* Add github actions tests for unstable ABI

updates:
- [github.com/asottile/pyupgrade: v2.25.0 → v2.26.0](https://github.com/asottile/pyupgrade/compare/v2.25.0...v2.26.0)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

* Restoring `const` removed from pytypes.h in PR #3254, adding tests reflective of user code that breaks when those `const` are removed.

* clang-tidy NOLINTs (and one collateral fix).

* Inserting PYBIND11_CONST_FOR_STRICT_PLATFORMS

* Trying `defined(__APPLE__)`

* Trying again: `auto it` for strict platforms.

* Adding NOLINTNEXTLINE(bugprone-macro-parentheses), expanding comments.

* Labeling all changes with `PR #3263`, for easy reference, and to make it easy to undo these changes if we decide to do so in the future.

Thanks Aaron for jumping in fixing this!

* Fix thread safety for pybind11 loader_life_support

Fixes issue: https://github.com/pybind/pybind11/issues/2765

This converts the vector of PyObjects to either a single void* or
a per-thread void* depending on the WITH_THREAD define.

The new field is used by each thread to construct a stack
of loader_life_support frames that can extend the life of python
objects.

The pointer is updated when the loader_life_support object is allocated
(which happens before a call) as well as on release.

Each loader_life_support maintains a set of PyObject references
that need to be lifetime extended; this is done by storing them
in a c++ std::unordered_set and clearing the references when the
method completes.

* Also update the internals version as the internal struct is no longer compatible

* Add test demonstrating threading works correctly.

It may be appropriate to run this under msan/tsan/etc.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Update test to use lifetime-extended references rather than
std::string_view, as that's a C++ 17 feature.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Make loader_life_support members private

* Update version to dev2

* Update test to use python threading rather than concurrent.futures

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Remove unnecessary env in test

* Remove unnecessary pytest in test

* Use native C++ thread_local in place of python per-thread data structures to retain compatability

* clang-format test_thread.cpp

* Add a note about debugging the py::cast() error

* thread_test.py now propagates exceptions on join() calls.

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* remove unused sys / merge

* Update include order in test_thread.cpp

* Remove spurious whitespace

* Update comment / whitespace.

* Address review comments

* lint cleanup

* Fix test IntStruct constructor.

* Add explicit to constructor

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* Removing NOLINT pointed out by Aaron.

* Removing another NOLINT.

* Enable clang-tidy readability-const-return

* PyTest functional

* Fix regression

* Fix actual regression

* Remove one more NOLINT

* Update comment

Fixes #3252

* Set __file__ constant when using eval_file

* Use const ref

* Use a move instead

* Revert

* Improve test

* Guard test with Python version

* Fix tests

* Dont support Python2 API

* Drop Python2 eval __file__ support

* Hack

* Semisupport Python2

* Take2

* Remove Python2 support

* Adding google-explicit-constructor to .clang-tidy

* clang-tidy explicit attr.h (all automatic)

* clang-tidy explicit cast.h (all automatic)

* clang-tidy detail/init.h (1 NOLINT)

* clang-tidy detail/type_caster_base.h (2 NOLINT)

* clang-tidy pybind11.h (7 NOLINT)

* clang-tidy detail/common.h (3 NOLINT)

* clang-tidy detail/descr.h (2 NOLINT)

* clang-tidy pytypes.h (23 NOLINT, only 1 explicit)

* clang-tidy eigen.h (7 NOLINT, 0 explicit)

* Adding 2 explicit in functional.h

* Adding 4 explicit in iostream.h

* clang-tidy numpy.h (1 NOLINT, 1 explicit)

* clang-tidy embed.h (0 NOLINT, 1 explicit)

* clang-tidy tests/local_bindings.h (0 NOLINT, 4 explicit)

* clang-tidy tests/pybind11_cross_module_tests.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/pybind11_tests.h (0 NOLINT, 2 explicit)

* clang-tidy tests/test_buffers.cpp (0 NOLINT, 2 explicit)

* clang-tidy tests/test_builtin_casters.cpp (0 NOLINT, 4 explicit)

* clang-tidy tests/test_class.cpp (0 NOLINT, 6 explicit)

* clang-tidy tests/test_copy_move.cpp (0 NOLINT, 7 explicit)

* clang-tidy tests/test_embed/external_module.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/test_embed/test_interpreter.cpp (0 NOLINT, 1 explicit)

* clang-tidy tests/object.h (0 NOLINT, 2 explicit)

* clang-tidy batch of fully automatic fixes.

* Workaround for MSVC 19.16.27045.0 C++17 Python 2 C++ syntax error.

* Add a missing noexcept to pytypes constructor.

Adds a few missing noexcept to PyType constructors for perf reasons.

* Revert exception ctor

Minor follow-on to PR #1334 (Fix enum value's __int__ returning non-int when underlying type is bool or of char type) (#3232)

* Minor tweaks.

* Restoring tests/pybind11_tests.h version from master, removing just the comment and empty line that was added in PR #3087; those were made obsolete by the pragma cleanup that concluded with PR #3186.

* More-to-the-point test for Python 3.

* Minor tweaks.

* Restoring tests/pybind11_tests.h version from master, removing just the comment and empty line that was added in PR #3087; those were made obsolete by the pragma cleanup that concluded with PR #3186.

* [ci skip] Restoring tests/test_enum.py from master.

* fix: memory leak in cpp_function (#3228)

* add a test case to check objects are deconstructed in cpp_function

* update the test case about cpp_function

* fix the test case about cpp_function: remove "noexcept"

* Actually calling func. CHECK(stat.alive() == 2); Manually verified that the new tests fails without the change in pybind11.h

* Moving new test to test_callbacks.cpp,py, with small enhancements.

* Removing new test from test_interpreter.cpp (after it was moved to test_callbacks.cpp,py). This restores test_interpreter.cpp to the current state on master.

* Using py::detail::silence_unused_warnings(py_func); to make the intent clear.

Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

updates:
- [github.com/asottile/pyupgrade: v2.24.0 → v2.25.0](https://github.com/asottile/pyupgrade/compare/v2.24.0...v2.25.0)
- [github.com/psf/black: 21.7b0 → 21.8b0](https://github.com/psf/black/compare/21.7b0...21.8b0)

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>

Adding `ssize_t_cast` to support passing `size_t` or `ssize_t` values where `ssize_t` is needed. (#3219)

* Trivial change to avoid (ssize_t) cast.

* Demo for safe_ssize_t idea.

* Removing safe_ssize_t.cpp (proof-of-concept code) to not upset the GHA Format workflow.

* Completing changes in pytypes.h

* New ssize_t_cast (better replacement for safe_ssize_t).

* clang-format-diff (no manual changes).

* bytes_ssize_t -Wnarrowing reproducer (see PR #2692).

* Backing out tuple(), list() ssize_t support, for compatibility with older compilers (to resolve link failures).

* Bug fix: missing `py::` for `py::ssize_t`

* Restoring tuple(), list() ssize_t support, but passing `size` by value, for compatibility with older compilers (to resolve link failures).

* Full test coverage of all functions with modified signatures.

* Use equivalent_integer for enum's Scalar decision

* Add test for char underlying enum

* Support translating bool type in enum's Scalar

* Add test for bool underlying enum

* Fix comment in test

* Switch from `PYBIND11_CPP20` macro to `PYBIND11_HAS_U8STRING`

* Refine tests

Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>

* Call PySys_SetArgv when initializing interpreter.

* Document argc/argv parameters in initialize_interpreter.

* Remove manual memory management from set_interpreter_argv in favor of smart pointers.

* Use size_t for indexers in set_interpreter_argv.

* Minimize macros for flow control in set_interpreter_argv.

* Fix 'unused variable' warning on Py2

* whitespace

* Define wide_char_arg_deleter outside set_interpreter_argv.

* Do sys.path workaround in C++ rather than eval.

* Factor out wchar conversion to a separate function.

* Restore widened_argv variable declaration.

* Fix undeclared widened_arg variable on some paths.

* Use delete[] to match new wchar_t[].

* Fix compiler errors

* Use PY_VERSION_HEX for a cleaner CVE-2008-5983 mode check.

* Fix typo

* Use explicit type for deleter so delete[] works cross-compiler.

* Always use PySys_SetArgvEx because pybind11 doesn't support pythons that don't include it.

* Remove pointless ternary operator.

* Use unique_ptr.reset instead of a second initialization.

* Rename add_program_dir_to_path parameter to clarify intent.

* Add defined() check before evaluating HAVE_BROKEN_MBSTOWCS.

* Apply clang-tidy fixes

* Pre-commit

* refactor: use const for set_interpreter_argv

* Try to fix const issue and allocate vector properly

* fix: copy strings on Python 2

* Applying clang-format-diff relative to master.

The only manual change is an added empty line between pybind11 and system `#include`s.

```
git diff -U0 --no-color master | python3 $HOME/clone/llvm-project/clang/tools/clang-format/clang-format-diff.py -p1 -style=file -i
```

Co-authored-by: Boris Staletic <boris.staletic@gmail.com>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: Henry Schreiner <henryschreineriii@gmail.com>
Co-authored-by: Ralf W. Grosse-Kunstleve <rwgk@google.com>

* reshape

* more tests

* Update numpy.h

* Update test_numpy_array.py

* array view

* test

* Update test_numpy_array.cpp

* Update numpy.h

* Update numpy.h

* Update test_numpy_array.cpp

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix merge bug

* Make clang-tidy happy

* Add xfail for PyPy

* Fix casting issue

* Fix formatting

* Apply clang-tidy

* Address reviews on additional tests

* Fix ordering

* Do a little more reordering

* Fix typo

* Try improving tests

* Fix error in reshape

* Add one more reshape test

* Fix bugs and add test

* Relax test

* streamlining new tests; removing a few stray msg

* Fix style revert

* Fix clang-tidy

* Misc tweaks:
* Comment: matching style in file (///), responsibility sentence, consistent punctuation.
* Replacing `unsigned char` with `uint8_t` for max consistency.
* Removing `1` from `array_view1` because there is only one.

* Partial clang-format-diff.

Co-authored-by: ncullen93 <ncullen.th@dartmouth.edu>
Co-authored-by: NC Cullen <nicholas.c.cullen.th@dartmouth.edu>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ralf Grosse-Kunstleve <rwgk@google.com>

* reshape

* more tests

* Update numpy.h

* Update test_numpy_array.py

* Update numpy.h

* Update numpy.h

* Update test_numpy_array.cpp

* [pre-commit.ci] auto fixes from pre-commit.com hooks

for more information, see https://pre-commit.ci

* Fix merge bug

* Make clang-tidy happy

* Add xfail for PyPy

* Fix casting issue

* Address reviews on additional tests

* Fix ordering

* Do a little more reordering

* Fix typo

* Try improving tests

* Fix error in reshape

* Add one more reshape test

* streamlining new tests; removing a few stray msg

Co-authored-by: ncullen93 <ncullen.th@dartmouth.edu>
Co-authored-by: NC Cullen <nicholas.c.cullen.th@dartmouth.edu>
Co-authored-by: Aaron Gokaslan <skylion.aaron@gmail.com>
Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Ralf Grosse-Kunstleve <rwgk@google.com>

Co-authored-by: Jouke Witteveen <j.witteveen@cosine.nl>

* Add py::raise_from to enable chaining exceptions on Python 3.3+

* Use 'raise from' in initialization

* Documenting the exact base version of _PyErr_FormatVFromCause, adding back `assert`s.

Co-authored-by: Dustin Spicuzza <dustin@virtualroadside.com>

* maint(clang-tidy): add a clang-tidy slicing check

* Add self + touch up readme

* Fix typo